"There is a 16 km (10 miles) thick layer of in equal density below the areas having similar density." Who expressed this view about Isostasy ?

Question

Accepted Answer

Joly expressed the view that there is a 16 km (10 miles) thick layer of unequal density below areas having similar density. This view aligns with Joly's concept of a substratum where density variations exist beneath the Earth's crust, influencing isostatic balance. Joly's work focused on the idea of a fluid or plastic substratum upon which the rigid crust floats, and the density variations within this substratum are key to understanding isostatic adjustments.

Here's why the other options are incorrect in the context of the given statement:

*   **Holmes:** Arthur Holmes is known for his contributions to radiometric dating and the theory of mantle convection. While he contributed significantly to understanding the Earth's interior, the specific statement about a 16 km thick layer of unequal density is not directly attributed to him in the context of isostasy. His work on mantle convection is related to broader Earth dynamics but doesn't specifically address this particular density layer concept as Joly did.

*   **Pratt:** Pratt's theory of isostasy focuses on the idea that the Earth's crust is made up of columns of equal mass but varying densities. Higher mountains are composed of less dense material, while lower areas are composed of denser material. This contrasts with the statement about a layer of *unequal* density *below* areas of similar density. Pratt's concept deals with density variations *within* the crustal columns themselves, not a distinct layer beneath.

*   **Airy:** Airy's theory of isostasy proposes that the Earth's crust floats on a denser mantle, like icebergs in water. Mountains have deeper "roots" extending into the mantle, while lower areas have shallower roots. While Airy's theory addresses the relationship between crustal thickness and elevation, it doesn't specifically focus on a 16 km thick layer of unequal density below areas of similar density. Airy's model emphasizes variations in crustal thickness, not density variations in a specific layer beneath areas of similar density.

Therefore, based on the provided information and the context of the question, Joly is the most appropriate answer because his work aligns with the concept of a substratum with density variations influencing isostatic balance, as described in the statement.